Method of training nitinol wire

ABSTRACT

A method of coating a preformed trainable material, such as nitinol wire, with a heat resistant substance, heat treating, and cooling to form a desired shape. The substance can be removed by various methods after heat treatment, depending upon the composition of the substance. The method includes forming a trainable material around a mold that dissolves, vaporizes, or can otherwise be removed. The method is useful for forming complicated shapes that would be expensive or impossible to form by conventional methods.

[0001] This application claims benefit to provisional application U.S.Serial No. 60/296,727 filed in the U.S. Jun. 11, 2001.

FIELD OF THE INVENTION

[0002] This invention relates to a method for training nitinol wire,particularly the training of nitinol wire into complicated shapes thatwould be expensive or impossible by conventional methods.

BACKGROUND OF THE INVENTION

[0003] Nitinol, a nickel-titanium alloy, is well known in the art forits superb elasticity. Nitinol wire and wire mesh can be permanentlyformed into a desired shape by a process called training. Trainingconsists of first manually manipulating the trainable material into thedesired shape and then heat treating it while holding it firmly in thatshape. The heat treatment consists of subjecting the material to a hightemperature for a particular amount of time and then cooling it. Fornitinol, this high temperature is usually between about 450 and 600° C.,and this time usually ranges from a few seconds to three minutes. Afterthe nitinol is subsequently cooled, it will maintain the desired shape.

[0004] Methods of heat treating are well known in the art. Heat treatinga material requires a uniform rate of heating and cooling to minimizeundesired stresses on the material. A method of heat treating andquenching complex geometries without distortion or cracking is taught inU.S. Pat. No. 4,789,410 by Parizek. It teaches the use of two salt bathsheld at different temperatures into which the material to be treated issubmerged at different times.

[0005] During the heat treatment, the nitinol must be held firmly in itsdesired shape, otherwise the shape of the nitinol will warp during theheat treatment. In order to overcome this warping and to provide a firmsupport for the nitinol during heat treatment, the standard method offorming nitinol into a desired shape is to first create a metal moldthat can withstand a high temperature. The mold consists at least of afirst piece and a second piece, the first piece able to fit snugly intothe second piece, and the two pieces able to lock together. The nitinolin a wire or wire mesh form is then sandwiched between the two piecesand then the pieces are pressed and locked together, thus giving thenitinol the desired shape. The entire mold with the nitinol inside isthen subjected to the heating process. For more complicated shapes, morethan two pieces may be used, but in each case every part of the nitinolis sandwiched between at least two of these pieces and remainssandwiched during the heating process.

[0006] Another method of reducing warpage during the heat treatment istaught in U.S. Pat. No. 6,210,500 by Zurfluh. It teaches a fixture thathas porous support walls that engage opposite sides of the material tobe heat treated. A liquid heating and cooling media is then flowedthrough the porous walls to heat treat the material while the supportwalls minimize warpage of the material.

[0007] One problem with conventional methods is that they are notconducive to certain shapes. For example, shapes that have an enclosedvolume cannot be easily formed using the conventional methods. This isbecause once the heat treatment has taken place, it is not possible toremove a solid metal mold from inside. One way to solve this problem isby using a collapsible inside mold, but this method is very expensiveand complicated. Another problem with this method is that somecomplicated shapes are not even conducive to such collapsible molds.

[0008] Another way to solve the problem of training materials intocomplicated shapes is by using a mold that is created from sand bound bya resin binder. The material can then be shaped around the sand mold andheat treated with the sand still inside. After the heat treatment, thesand mold can be broken down and removed, for example, by vibration. Ameans for processing and reusing sand molds is described in U.S. Pat.No. 5,901,775 by Musschoot et al.

[0009] One problem with such a method is that the sand mold is verycrude and the resulting trained material must be processed or machinedin order to remove the roughness and imperfection resulting from thesand mold. Another problem is that the external part of the mold, madeof metal or sand (depending on the application) is bulky and heavy. Thisresults in three further problems: high expense of the external mold;high expense of continually heating and cooling mold materials; highexpense of large heat treating baths or ovens and processing equipment;difficulty in achieving a uniform rate of heating and cooling due to thethickness of the external part of the mold. This makes the coolingprocess and cooling rate harder to control. The cooling rate must becarefully controlled. Nitinol must be cooled to a point at which itretains the desired shape without the support of the mold, but if it iscooled too quickly, it can become unacceptably brittle.

SUMMARY OF THE INVENTION

[0010] One object of the present invention is to overcome thedisadvantages of the known art described above.

[0011] Another object of the present invention is to provide a method oftraining a heat settable or trainable material such as nitinol in adesired shape which does not warp or change shape during the heattreatment process.

[0012] Another object of the present invention is to provide a method oftraining nitinol in complicated shapes.

[0013] Another object of the present invention is to provide a method oftraining nitinol in a desired shape that includes at least one hole orcore through which a solid mold cannot exit.

[0014] Another object of the present invention is to provide a method oftraining nitinol inexpensively and without the use of heavy, expensivemolds.

[0015] The present invention provides a method of training a trainablematerial, comprising the steps of forming the material into a desiredshape, applying a heat-resistant substance to the material capable ofholding the material in the desired shape, heating the material to atemperature and time sufficient for the material to retain the shape,cooling the material, and removing the substance from the material. In apreferred aspect, the material permanently retains its shape afterremoving the substance from the material, and the material comprises anickel titanium alloy, such as a nitinol alloy. In another preferredaspect, the substance remains in a solid form at the temperature, andcomprises one of plaster of paris, concrete, a ceramic, paint, and glue.A preferred time and temperature are, respectively, greater than onesecond and less than about 10 minutes, and greater than about 450° C.and less than about 600° C. In another preferred aspect, the coolingstep comprises cooling with the use of a gas, such as air or compressedair, or with the use of a liquid, such as water.

[0016] In another preferred aspect, the step of forming the materialcomprises forming the material with a mold comprising a plastic, such asan ethylene, that has been created by injection molding. In anotherpreferred aspect, the step of removing the substance comprisesdissolving the substance in a dissolving substance, e.g., water. Inanother preferred aspect, the step of removing the substance comprisesone of chemically reacting the substance with a reacting substance andbreaking the substance—e.g., by vibrating the substance.

[0017] The present invention also provides a method of training atrainable material, comprising the steps of forming a mold of a desiredshape, forming the material with the use of the mold, applying aheat-resistant substance to the material capable of holding the materialin the desired shape, heating the material to a temperature and timesufficient for the material to retain the shape, cooling the material,and removing the substance from the material. In a preferred aspect ofthe present invention, at least part of the mold is removed prior toheating the material. In another preferred aspect, the materialpermanently retains its shape after removing the substance from thematerial, and the material comprises a nickel titanium alloy, such as anitinol alloy. In yet another preferred aspect, the heat-resistantsubstance is in a non-solid form that hardens after application, andremains in a solid form at the temperature, and comprises one of plasterof paris, concrete, a ceramic, paint, and glue. A preferred time andtemperature are, respectively, greater than one second and less than 10minutes, and greater than about 450° C. and less than about 600° C. Inanother preferred aspect, at least a part of the mold is retained afterapplying the heat resistant substance and is pyrolyzed during theheating of the material. In another preferred aspect, the cooling stepcomprises cooling with the use of a gas, such as air or compressed air,or with the use of a liquid, such as water.

[0018] In another preferred aspect, the step of heating the materialcomprises heating at least one piece of the mold, and the piecevaporizes at a vaporization temperature below the temperature, and thepiece vaporizes completely. In another preferred aspect, the step offorming the material comprises forming the material with a moldcomprising a plastic, such as an ethylene, that has been created byinjection molding. In another preferred aspect, the step of removing thesubstance comprises dissolving the substance in a dissolving substance,such as water. In another preferred aspect, the step of removing thesubstance comprises one of chemically reacting the substance with areacting substance and breaking the substance—e.g., by vibrating thesubstance. In another preferred aspect, the piece is removed from thematerial, and it is removed by one of dissolving the piece in a molddissolving substance, such as water, chemically reacting the piece in amold reacting substance, and breaking the piece—e.g., by vibrating thepiece. In another preferred aspect, the step of removing the substanceand removing the piece occur at substantially the same time.

[0019] These objects and advantages, as well as other objects andadvantages, of the present invention will be set forth in thedescription that follows, and in part will be readily apparent to thoseskilled in the art from the description and drawings, or may be learnedby practice of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] FIGS. 1 to 6 show nitinol wire structures formed by the method ofthe invention.

[0021]FIG. 7 shows a collection of nitinol wire structures and theirrelative sizes.

[0022] FIGS. 8 to 12 show plans and dimensions for a complicated nitinolwire structure that can be trained by the method of the invention.

[0023]FIG. 13 is a sectional view of a mold assembly suitable for use inthe method of the invention.

[0024]FIGS. 14A and 14B are side and cross-sectional views,respectively, of a nitinol medical device formed by the method of thisinvention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0025] The present invention avoids the above problems by providing amethod of coating a pre-formed trainable material with an inexpensiveheat-resistant substance that can be removed after the heat treatment.The present invention also provides a method of forming a trainablematerial around a mold that can either vaporize during the heattreatment or can be removed after the heat treatment.

[0026] The present invention is usable with any material that can beformed into a desired shape and then set or trained by heat. While thefollowing preferred embodiments have been described with respect tonitinol and its alloys, it should be understood that other materials,such as steel and spring wire, are within the scope of the invention.

[0027] The present invention relates to a method for training nitinolwire, particularly the training of nitinol wire into complicated shapesthat may be expensive or impossible by conventional methods.

[0028] In a preferred embodiment, a practice of the method of theinvention begins with forming a trainable material into a desired shape.In this embodiment, the trainable material is nitinol, a nickel-titaniumalloy, but the practice of this method on other trainable materials willbe apparent to one skilled in the art. The nitinol can be in the form ofa wire, a wire mesh, braided wire, a sheet, a tube, a slotted tube, orany other form that can be manipulated into a desired shape. The formingof the nitinol can be accomplished in any number of ways. In the mostbasic embodiment, the nitinol can be formed by hand into a desiredshape. One skilled in the art will recognize the many possibleapparatuses available to form a wire or sheet into a desired shape. In apreferred embodiment, a mold is initially used to form the nitinol intothe desired shape. Because of the inherent elasticity of nitinol, thenitinol will spring back into its trained shape unless held in thedesired shape throughout the training process.

[0029] The nitinol is held in its desired shape with the use of apreferably nonsolid heat-resistant substance that hardens with time.Examples of such a substance include plaster of paris, concrete, cement,and ceramics, although similarly useful substances would be apparent toone skilled in the art. Other examples include resins, glues, adhesives,paints, and varnishes. The heat-resistant substance is then appliedeither when or after the mold is applied to the nitinol. More than onecoat of the substance can be applied, and the thickness of each coat mayvary, depending on the strength required to hold the nitinol in itsdesired shape. After the substance hardens, the substance will hold thenitinol in the desired shape, and the mold can be removed from thenitinol prior to the heat treatment step. In this embodiment, it is themold that forms the nitinol into its desired shape, and theheat-resistant substance that holds the nitinol in its desired shapeafter the mold has been removed.

[0030] One advantage of the present invention is the ability to form thenitinol first, and then to hold it in place for the heat treatment step.In conventional methods, the forming and holding takes place at the sametime and with the same implement, such as a mold. While a mold could beused with the present invention to initially form the nitinol, theforming step is independent of the holding step. Therefore, theimplement that was used to form the nitinol (e.g., a mold) does notnecessarily enter the heat treatment step with the nitinol. It will beapparent to one skilled in the art that many other implements could beused to form the nitinol.

[0031] In a preferred embodiment, a mold made of an injection moldedpiece of polyethylene is used to form the nitinol. Injection molding isan inexpensive, efficient process that creates precision molds, andpolyethylene is an inexpensive, easy-to-use plastic. However, it wouldbe apparent to one skilled in the art that many other possible materialsand mold-creating methods could be used to create the mold. A moldcould, for example, be created out of a metal, ceramic, or anothersuitable plastic.

[0032] The mold consists at least of a first piece and a second piece,the first piece able to fit snugly into the second piece, and the twopieces are able to fit together and may lock together. Also, one or bothof the pieces must contain ribs, channels, or other spaces so that, whenthey are locked together, there is sufficient space for both the nitinoland the heat-resistant substance. The nitinol, preferably in a wire orwire mesh form, is then sandwiched with the heat-resistant substancebetween the two pieces and then the pieces are pressed and lockedtogether, thus giving the nitinol the desired shape. For morecomplicated shapes, more than two pieces may be used. Preferably, ineach case, every part of the nitinol is sandwiched with theheat-resistant substance between at least two of these pieces. However,in some instances, part of the nitinol may remain free of the mold.

[0033] In this embodiment, the heat-resistant substance is then allowedto harden, and then the mold is removed from the nitinol. The nitinol isthen held in its desired shape by the heat-resistant substance that hashardened around it.

[0034] In another embodiment, the nitinol is formed by some means otherthan the mold mentioned, and then it is dipped into the heat-resistantsubstance which is subsequently allowed to harden. For example, in orderto form a nitinol wire mesh into a flat sheet and hold it in this shapefor heat treating, a nitinol wire mesh could be stretched out over ahard surface, each of its comers attached to the surface by conventionalmeans such as a clip or screws. The entire surface could then be dippedin the heat-resistant substance, or the heat-resistant substance couldbe poured or sprayed onto the surface. When the substance hardened, thesubstance-coated nitinol could then be detached from the surface byremoving the clips or screws. The nitinol would then be held in itsdesired shape by the heat-resistant substance and ready to be heattreated.

[0035] In a preferred embodiment, the substance-coated nitinol is thensubjected to a heat treatment, whereby the nitinol is heated to atemperature at which the nitinol is trained. At this temperature, thenitinol loses its elasticity and assumes the desired shape withoutresistance. The temperature at which this happens is approximately 530°C., although it can happen in the approximate range of about 450° C. toabout 600° C. In this embodiment, the heat-resistant substance remainsin solid form at this temperature, continuing to hold the nitinol in thedesired shape. The nitinol is then held at this temperature for enoughtime to allow the nitinol to assume its desired shape, and then it iscooled. The required amount of time generally ranges from about onesecond to ten minutes, with anything beyond ten minutes generally beingunnecessary. The cooling of the nitinol is required to allow it toachieve elasticity. The cooling rate should be fast enough that theprocess is efficient and not wasteful of time. However, if the coolingrate is too fast, thermal stresses arise in the nitinol that cause it tobe brittle. Because of the benefits of the nitinol's superelasticity,embrittlement should be avoided. One skilled in the art of trainingmaterials such as nitinol can readily determine suitable cooling timesand temperatures.

[0036] The cooling can take place with the use of many possible heattransfer media. The type of media used will depend on the complexity andsize of the desired shape, and also the thickness of the heat-resistancesubstance layer on the nitinol, because the heat-resistant substance maybe an insulator. In the conventional method of heat treatment, a verydense, conductive heat transfer medium is used because the molds areusually very thick. However, because the heat-resistant substance layercan be very thin in comparison to conventional molds, the heat transferrate through such a layer may be much higher than in conventional molds.For this reason, a heat transfer medium that is low in density or heatconductivity may be useful in the cooling process. In a preferredembodiment, the heat transfer medium for cooling process is air orcompressed air. Air is inexpensive, compared to a salt bath, forexample. In another preferred embodiment, water is used as the coolingmedium, because it has a high heat transfer rate. Water is used when theheat-resistant substance is thick, in order to increase efficiency ofthe method, but care should be taken to make sure the nitinol is notembrittled by the faster cooling rate of water. Many other possiblegaseous or liquid heat exchange media for the cooling process will beapparent to one skilled in the art.

[0037] After the cooling process, the heat-resistant substance isremoved. The substance can be removed in many different ways. In oneembodiment, the substance is removed by dissolving it in a dissolvingmedium, such as water. For example, the substance-coated nitinol cansimply be dipped in a bath of water, or water can be sprayed on to thesubstance-coated nitinol until the substance is completely removed.Other dissolving media can be used, but care should be taken that thereis no reaction between the dissolving medium and the nitinol itselfunless, of course, such reaction is desired. Water works well, forexample, in dissolving plaster of paris.

[0038] In another embodiment, the substance is simply broken off of thenitinol. This breaking process can be accomplished in many ways thatwill be apparent to one skilled in the art. For example, thesubstance-coated nitinol can be struck with a hammer-type or wedge-typetool. Because the heat-resistant substance is brittle but the nitinol iselastic, this method of breaking the substance will cause the substanceto shatter with the nitinol remaining intact. Another example is the useof vibrations to break the substance. The substance-coated nitinol canbe subjected to intense, high-frequency sound waves in a gas or liquidmedium, causing the brittle heat-resistant substance to be pulverized.Again, the elastic nitinol will remain intact.

[0039] In another embodiment, the heat-resistant substance is removed bychemical reaction with a chemical reacting substance. The application ofsuch a reacting substance is similar to the application of a dissolvingsubstance, discussed above, and care should be taken that there is noreaction between the reacting substance and the nitinol itself unless areaction is desired.

[0040] In another preferred embodiment, the nitinol is first formed withthe use of a mold. The heat-resistant substance is applied either duringor after the application of the mold to the nitinol, as discussedpreviously. However, instead of removing all pieces of the mold, atleast one piece of the mold remains with the substance-covered nitinolthrough at least part of the heat treating process and, if necessary, isremoved after the heat treating process. This embodiment is useful whenthe desired shape has at least one enclosed volume through which a solidmold would not be able to exit after the heat treating process.

[0041] Referring to FIGS. 1 to 12, all of the objects have shapes thatwould not be easily formed with conventional means. For example, FIGS. 1to 7 show various shapes that are convoluted or have enclosed volumes.If a solid mold piece had been used on the inside of the object, thatpiece would have been difficult or impossible to remove after the heattreating process without breaking or tearing the object open. In suchembodiments, as described below, where at least a part of the moldremains prior to heating and is destructively removed during heatingsuch as by pyrolysis or after heating such as by dissolution ormechanical destruction the remaining mold/mold piece is considered to bea “sacrificial mold.”

[0042]FIG. 1 shows tubular material trained into a closed ended cylinderwith both ends folded inwardly into the interior of the closed cylinder.The ends of the braided material are substantially gathered so as tominimize the passageway from the interior of the structure to theexterior of the structure.

[0043]FIG. 2 shows the structure dimensioned in FIG. 10. FIG. 2 showstubular material trained into a cylindrical tube of mesh material with aspherical bulge along the axis of the tubular mesh material.

[0044]FIG. 3 shows tubular material trained into a spheroid shape withone end of the tube folded inwardly into the interior of the spheroidand the opposite end of the tubular material trained into a looselygathered configuration external to the spheroid shape.

[0045]FIG. 4 shows tubular material trained into a spheroid shape withboth ends of the tubular material trained into loosely gatheredconfigurations external to the spheroid shape.

[0046]FIG. 5 shows a cut length of tubular material trained into acylindrical open ended cylinder with both cut ends folded inwardly intothe interior of the cylinder and expanded to lie against the interiorwall of the open cylinder. The length of the open cylinder has beentrained to assume a curvilinear shape with the open ends of the cylindersmaller in diameter than the midlength transverse diameter of thecylinder.

[0047]FIG. 6 shows a cut length of tubular material trained into asubstantially closed ended cylinder with both cut ends folded inwardlyinto the interior of the cylinder and with both ends of the tubularmaterial trained into loosely gathered configurations. One of theinwardly folded ends is substantially coaxial with the end perimeter ofthe closed ended cylinder and the opposite inwardly folded end issubstantially eccentric to the end perimeter of the closed endedcylinder. The length of the cylinder has been trained to assume acurvilinear shape with one end of the cylinder smaller in diameter thanthe opposite end of the cylinder.

[0048]FIG. 7 illustrates objects 10, 20, 30, 40, 50, 60, 70, 80, 90, and100 formed from nitinol wire by the method of this invention. Theobjects have various shapes that are difficult to form by conventionalmethods.

[0049] Object 10 is an open ended substantially cylindrical tubular meshof trained material. Object 20 is the structure described in FIG. 1.Object 30 is an on-axis end view of the structure described in FIG. 2.Object 40 is a closed spherical structure of trained material. Object 50is a side view of the structure described in FIG. 2. Object 60 is astructure similar to that described in FIG. 6. Object 70 is thestructure described in FIG. 3. Object 80 is a side view of a structuresimilar to that described in FIG. 2 with smaller openings at the ends ofthe trained structure. Object 90 is the structure described in FIG. 5.Object 100 is a mesh of material trained into closed ended cylinder.

[0050]FIG. 8 shows a side view of a complex cylindrical shape formed bythe method of this invention, and FIG. 9 is a top view. This cylinder isopen at both bottom and top, and illustrates a shape for which theprocess of this invention is advantageous, i.e., larger in its centersection than at the top and bottom. FIG. 10 shows the dimensions of thiscomplex cylinder. The axial radius R1 is 0.5 inch (1.27 cm), thediameter a of the top opening is 0.527 inch (1.34 cm), the length e is1.05 inch (2.67 cm), and the width b is 1.25 inches (3.17 cm). Segment hhas aradius R2 of 0.156 inch (0.4 cm). The top end segment c is 0.1 inch(0.25 cm) long and the body segment d is 0.85 inch (2.16 cm) long.

[0051] In this embodiment, at least one sacrificial piece of the moldremains with the substance-covered nitinol, particularly that piece orthose pieces that would otherwise be difficult to remove after the heattreating process. In the case of FIG. 1, there would be one internalpiece that would otherwise be difficult to remove after the heattreating process, so this would be the piece that would remain in thispreferred embodiment, while the external piece or pieces would beremoved before the heat treating process. For this reason, the followingdescription will differentiate between the internal and external pieces.However, one skilled in the art would realize other types of mold piecescould exist—besides internal and external—and that some external piecescould remain with the nitinol and thus be sacrificial while someinternal pieces could be removed, without deviating from the spirit ofthe invention.

[0052]FIG. 11 shows a top view of a sphere, having diameter f of 0.5inch (1.27 cm), and FIG. 12 shows a side view of an ovoid, in whichopening g is 0.25 inch (0.64 cm) wide, and a segment i has a radius R3of 0.25 inch (0.64 cm).

[0053]FIG. 13 is a cross-sectional view of a mold assembly 100 which canbe used in the method of this invention. Mold assembly 100 includesportions 1 a and 1 b which contain trainable material 2 such as nitinolwire and heat resistant substance 3.

[0054] In a preferred embodiment, the mold is created from polyethyleneby the injection molding process. The nitinol is formed as describedpreviously and the heat-resistant substance is applied and hardened asdescribed previously. The external piece or pieces of the mold are thenremoved from the substance-coated nitinol while at least one internalsacrificial piece remains. The nitinol—coated with the heat-resistantsubstance and enclosing at least one internal mold piece—is thensubjected to the heat treatment. The polyethylene internal mold piece,which vaporizes and burns (i.e., pyrolyzes) at a temperature lower thanthe training temperature of nitinol, will then burn. The heat treatmentcontinues until all remains of the sacrificial mold have vaporized orcombusted, or until enough of the mold has vaporized or combusted toallow the remains of the mold to pass through the exit of the shape'senclosure. The substance-coated nitinol is then subjected to the coolingprocess and substance-removal process as discussed previously. It willbe apparent to one skilled in the art that the mold can be made of manypossible substances that vaporize or burn at a temperature lower thanthe training temperature of nitinol. For example, other types ofplastics could be used.

[0055] In another embodiment, the sacrificial mold is created from asubstance that can be easily dissolved, broken, or chemically reactedwith another substance, as previously discussed. For example, thesacrificial mold could be created of the same substance as theheat-resistant substance and could be removed at the same time, andthrough the same process, as the heat-resistant substance. For example,the mold could be created from plaster of paris, and the nitinol couldbe coated with plaster of paris according to the process described.After the heat treating process, both the internal sacrificial moldpiece and the heat-resistant substance could be removed at substantiallythe same time by dissolving them in water. They could also be removed atsubstantially the same time by pulverizing them with a powerfulhigh-frequency sound wave. In addition, the sacrificial mold could becreated of a substance different than the heat-resistant substance, withtheir respective removal processes either the same or different.

[0056] The method of this invention can be used to train a trainablematerial for many different applications. One such application is shownin FIGS. 14A and 14B which show a filter device for use in a lumen of ahuman body such as a vessel in the vascular system. FIG. 14A is a sideview of device 110 and FIG. 14B is a cross-sectional view. Device 110 iscomprised of a cylinder of trainable mesh material 18 trained into abell like shape with one end open and one end closed. The ends of thetrainable material are contained within elements 14 and 16 which may besolid or tubular. In use device 110 is carrier by an elongate supportmember which may be a guide wire. One of the elements 14 and 16 is fixedto the support member and the other slides over the support member. Thisconfiguration allows the device to be delivered through the lumen in areduced diameter configuration when elements 14 and 16 are spaced apartand to be expanded in the lumen by moving elements 14 and 16 closertogether.

[0057] While a number of preferred embodiments of the present inventionhave been described, it should be understood that various changes,adaptations, and modifications may be made therein without departingfrom the spirit of the invention and the scope of the appended claims.As used herein and in the following claims, articles such as “the,” “a,”and “an” can connote the singular or plural.

What is claimed is:
 1. A method of training a trainable material,comprising: forming the trainable material into a desired shape;applying a heat-resistant substance to the trainable material capable ofholding the material in the desired shape; heating the trainablematerial to a temperature and for a time sufficient for the trainablematerial to retain the shape; cooling the trainable material; andremoving the heat-resistant substance from the trainable material.
 2. Amethod as claimed in claim 1, wherein the heat-resistant substance is ina non-solid form that hardens after application.
 3. A method as claimedin claim 1, wherein the trainable material permanently retains theshape.
 4. A method as claimed in claim 1, wherein the trainable materialcomprises a nickel titanium alloy.
 5. A method as claimed in claim 4,wherein the nickel titanium alloy is a nitinol alloy.
 6. A method asclaimed in claim 1, wherein the heat-resistant substance comprisesplaster of paris.
 7. A method as claimed in claim 1, wherein theheat-resistant substance comprises concrete.
 8. A method as claimed inclaim 1, wherein the heat-resistant substance comprises a ceramic.
 9. Amethod as claimed in claim 1, wherein the heat-resistant substancecomprises a paint.
 10. A method as claimed in claim 1, wherein theheat-resistant substance comprises a glue.
 11. A method as claimed inclaim 1, wherein the temperature is between about 450° C. and about 600°C.
 12. A method as claimed in claim 1, wherein the heat-resistantsubstance remains in a solid form at the temperature.
 13. A method asclaimed in claim 1, wherein in the heating step, the time is between onesecond and ten minutes.
 14. A method as claimed in claim 1, wherein thestep of cooling the trainable material comprises cooling the trainablematerial with a gas.
 15. A method as claimed in claim 14, wherein thegas is air.
 16. A method as claimed in claim 15, wherein the air iscompressed.
 17. A method as claimed in claim 1, wherein the step ofcooling the trainable material comprises cooling the trainable materialwith a liquid.
 18. A method as claimed in claim 17, wherein the liquidis water.
 19. A method as claimed in claim 1, wherein the step offorming the trainable material comprises forming the material with amold.
 20. A method as claimed in claim 19, wherein the mold comprises aplastic.
 21. A method as claimed in claim 20, wherein the mold has beencreated by injection molding.
 22. A method as claimed in claim 21,wherein the plastic is an ethylene.
 23. A method as claimed in claim 1,wherein the step of removing the heat-resistant substance comprisesdissolving the heat-resistant substance in a dissolving substance.
 24. Amethod as claimed in claim 23, wherein the dissolving substance iswater.
 25. A method as claimed in claim 1, wherein the step of removingthe heat-resistant substance comprises breaking the heat-resistantsubstance.
 26. A method as claimed in claim 25, wherein the breaking ofthe heat-resistant substance comprises vibrating the heat-resistantsubstance.
 27. A method as claimed in claim 1, wherein removing theheat-resistant substance comprises chemically reacting theheat-resistant substance with a reacting substance.
 28. A method oftraining a trainable material, comprising: forming a mold of a desiredshape; forming the trainable material into the desired shape with theuse of the mold; applying a heat-resistant substance to the trainablematerial capable of holding the trainable material in the desired shape;heating the trainable material to a temperature and for a timesufficient for the trainable material to retain the shape; cooling thetrainable material; and removing the heat-resistant substance from thetrainable material.
 29. A method as claimed in claim 28, furthercomprising removing at least a part of the mold prior to heating thetrainable material.
 30. A method as claimed in claim 28, wherein theheat-resistant substance is applied in a non-solid form that hardensafter application.
 31. A method as claimed in claim 28, wherein thetrainable material permanently retains the shape.
 32. A method asclaimed in claim 28, wherein at least a part of the mold is retainedafter applying the heat resistant substance and the at least the part ispyrolyzed during the heating of the trainable material.
 33. A method asclaimed in claim 28, wherein the trainable material comprises a nickeltitanium alloy.
 34. A method as claimed in claim 33, wherein the nickeltitanium alloy is a nitinol alloy.
 35. A method as claimed in claim 28,wherein the heat-resistant substance comprises plaster of paris.
 36. Amethod as claimed in claim 28, wherein the heat-resistant substancecomprises concrete.
 37. A method as claimed in claim 28, wherein theheat-resistant substance comprises a ceramic.
 38. A method as claimed inclaim 28, wherein the heat-resistant substance comprises a paint.
 39. Amethod as claimed in claim 28, wherein in the applying step, theheat-resistant substance comprises a glue.
 40. A method as claimed inclaim 28, wherein in the heating step, the temperature is between about450° C. and about 600° C.
 41. A method as claimed in claim 28, whereinin the heating step, the heat-resistant substance remains in a solidform at the temperature.
 42. A method as claimed in claim 28, wherein inthe heating step, the time is between one second and ten minutes.
 43. Amethod as claimed in claim 28, wherein the step of cooling the trainablematerial comprises cooling the trainable material with a gas.
 44. Amethod as claimed in claim 43, wherein the gas is air.
 45. A method asclaimed in claim 44, wherein the air is compressed.
 46. A method asclaimed in claim 28, wherein the step of cooling the trainable materialcomprises cooling the trainable material with a liquid.
 47. A method asclaimed in claim 46, wherein the liquid is water.
 48. A method asclaimed in claim 28, wherein the mold has at least two pieces andfurther wherein the step of heating the trainable material comprisesheating at least one piece of the mold.
 49. A method as claimed in claim48, wherein the at least one piece vaporizes at a vaporizationtemperature below the temperature.
 50. A method as claimed in claim 49,wherein the at least one piece completely vaporizes during the time. 51.A method as claimed in claim 49, wherein the at least one piececomprises a plastic.
 52. A method as claimed in claim 51, wherein the atleast one piece has been created by injection molding.
 53. A method asclaimed in claim 51, wherein the plastic is an ethylene.
 54. A method asclaimed in claim 28, wherein the step of removing the heat-resistantsubstance comprises dissolving the heat-resistant substance in adissolving substance.
 55. A method as claimed in claim 54, wherein thedissolving substance is water.
 56. A method as claimed in claim 28,wherein the step of removing the heat-resistant substance comprisesbreaking the heat-resistant substance.
 57. A method as claimed in claim56, wherein the breaking of the heat-resistant substance comprisesvibrating the heat-resistant substance.
 58. A method as claimed in claim28, wherein the step of removing the heat-resistant substance compriseschemically reacting the heat-resistant substance with a reactingsubstance.
 59. A method as claimed in claim 48, further comprising thestep of removing the at least one piece from the trainable material. 60.A method as claimed in claim 59, wherein the step of removing the piececomprises dissolving the at least one piece in a mold dissolvingsubstance.
 61. A method as claimed in claim 60, wherein the molddissolving substance is water.
 62. A method as claimed in claim 59,wherein the step of removing the at least one piece comprises breakingthe at least one piece.
 63. A method as claimed in claim 62, wherein thebreaking of the piece comprises vibrating the piece.
 64. A method asclaimed in claim 59, wherein the step of removing the piece compriseschemically reacting the piece with a mold reacting substance.
 65. Amethod as claimed in claim 59, wherein the step of removing theheat-resistant substance and removing the at least one piece occur atsubstantially the same time.